\documentclass[11pt]{article}
\usepackage{array}
\newcommand{\PreserveBackslash}[1]{\let\temp=\\#1\let\\=\temp}
\newcolumntype{C}[1]{>{\PreserveBackslash\centering}p{#1}} %居中
\newcolumntype{R}[1]{>{\PreserveBackslash\raggedleft}p{#1}} % 右对齐
\newcolumntype{L}[1]{>{\PreserveBackslash\raggedright}p{#1}} % 左对齐
\begin{document}
\begin{table}[ht!]
	\begin{tabular}{|C{30 mm}|L{30 mm}| R{30 mm}|}\hline
		The tabularx package provides for the X columntype and the siunitx enables to use the S columntype. & The tabularx package provides for the X columntype and the siunitx enables to use the S columntype. & The tabularx package provides for the X columntype and the siunitx enables to use the S columntype.\\ \hline
	\end{tabular}
\end{table}
\end{document}
